Waste water treatment plants are used to treat waste water such that undesired objects, particles, organic substances, chemicals etc. are removed from the waste water prior to its emission into nature. One unwanted chemical is phosphate which is present in waste water from industries and house holds.
Phosphate may be removed by subjecting the waste water to a biological process comprising Polyphosphate-Accumulating Organisms which under the right conditions accumulate polyphosphate. One desirable feature of Polyphosphate-Accumulating Organisms is that they are capable of consuming large amounts of phosphate when subjected to the right series of conditions. However, Polyphosphate-Accumulating Organisms compete with Glycogen-Accumulating Organisms for the same organic material. This is undesirable in waste water treatment processes, as Glycogen-Accumulating Organisms do not provide the favourable phosphate removing capabilities which are associated with Polyphosphate-Accumulating Organisms. It has been found that the ratio of Glycogen-Accumulating Organisms relative to the total amount of Glycogen-Accumulating Organisms and Polyphosphate-Accumulating Organisms is higher in warmer climates than in colder climates, and thus the challenge in dealing with Glycogen-Accumulating Organisms is especially relevant in warmer climates. Attempts have been made to give Polyphosphate-Accumulating Organisms a competitive advantage, but no successful results have been achieved so far.
Background art may be found in WO 2008/046139 which discloses a biological process for reducing the levels of nitrogen and phosphorous in wastewater, wherein said wastewater comprises at least 100 mg/L total nitrogen wherein said process comprises feeding said wastewater into a reaction vessel in at least two steps, wherein said reaction vessel comprises an active biomass comprising nitrifying and denitrifying organisms and polyphosphate accumulating organisms (PAOs), wherein at least the first feed step is followed by a non-aerated period of sufficient duration to result in sufficiently low concentrations of nitrate and nitrite species in the wastewater to allow for accumulation of polyhydroxyalkanoates in the PAOs, and at least the first non-aerated period is followed by an aerated period of sufficient duration to allow for ammonium oxidation by the nitrifying organisms and assimilation by the PAOs of at least a portion of the phosphorous in the wastewater.
It is an object of one or more embodiments of the present invention, to provide a method which provides the Polyphosphate-Accumulating Organisms with a competitive advantage over Glycogen-Accumulating Organisms.
Moreover, it is an object of one or more embodiments of the present invention, to provide an improved method for removing phosphate in waste water.